Autofocus Imaging Device

This patent document claims the priority and benefits of Korean patent application No. 10-2024-0064544, filed on May 17, 2024, the disclosure of which is incorporated herein by reference in its entirety as part of the disclosure of this patent document.

The technology and implementations disclosed in this patent document generally relate to an imaging device for performing an autofocus function.

An imaging device is a device including an imaging circuit that captures optical images by converting light into electrical signals using a photosensitive semiconductor material which reacts to light. With the development of automotive, medical, computer and communication industries, the demand for high-performance imaging devices is increasing in various fields such as smart phones, digital cameras, game machines, IoT (Internet of Things), robots, security cameras and medical micro cameras.

The imaging devices may be roughly divided into CCD (Charge Coupled Device) imaging circuits and CMOS (Complementary Metal Oxide Semiconductor) imaging circuits. The CCD imaging circuits offer a better image quality, but they tend to consume more power and are larger as compared to the CMOS imaging circuits.

The CMOS imaging circuits are smaller in size and consume less power than the CCD imaging circuits. Furthermore, CMOS imaging circuits are fabricated using the CMOS fabrication technology, and thus photosensitive elements and other signal processing circuitry can be integrated into a single chip, enabling the production of miniaturized imaging circuits at a lower cost.

Various embodiments of the present disclosure relate to an imaging device for providing a phase-difference autofocus (PDAF) function that reduces the influence of noise, and a method for operating the same.

In accordance with an embodiment of the present disclosure, an imaging device may include an evaluation value calculator configured to calculate an evaluation value set including evaluation values corresponding to candidate parallaxes based on a phase image set; and a parallax calculator configured to calculate a target parallax based on the evaluation value set, the target parallax representing a phase shift value that allows to minimize a difference between phase images corresponding to phase signals with respect to an object to be imaged. Each of the evaluation values indicates a degree of certainty that the candidate parallax corresponding to each evaluation value is the target parallax.

In some implementations, the imaging device may further include: an imaging circuit that includes a lens and is configured to collect a phase signal pair including a first phase signal for an object and a second phase signal for the object, wherein the phase image set includes a first phase image corresponding to the first phase signal and a second phase image corresponding to the second phase signal.

In some implementations, the target parallax controls an in-focus position of the lens so that the first phase image and the second phase image coincide with each other.

In some implementations, the evaluation value calculator may be configured to calculate the evaluation value set based on a sum of absolute differences (SAD) between the first phase image and the second phase image.

In some implementations, the evaluation value calculator may be configured to calculate the evaluation value set based on a sum of square differences (SSD) between the first phase image and the second phase image.

In some implementations, the evaluation value calculator may be configured to calculate the evaluation value set based on phase correlation between the first phase image and the second phase image.

In some implementations, the evaluation value calculator may be configured to calculate the evaluation value set based on cross-correlation between the first phase image and the second phase image.

In some implementations, the imaging device may further include: an image generator configured to generate the phase image set based on the phase signal pair.

In some implementations, the image generator may be configured to generate a plurality of time phase image sets based on a plurality of phase signal pairs collected at different times; the evaluation value calculator may be further configured to calculate a plurality of time evaluation value sets respectively corresponding to the plurality of time phase image sets; and the parallax calculator may be further configured to calculate the target parallax based on the plurality of time evaluation value sets.

In some implementations, the image generator may be further configured to generate a plurality of region phase image sets based on one phase signal pair collected at an arbitrary time; the evaluation value calculator may be further configured to calculate a plurality of region evaluation value sets corresponding to the plurality of region phase image sets; and the parallax calculator may be configured to calculate the target parallax based on the plurality of region evaluation value sets.

In some implementations, the imaging circuit may be configured to transmit the phase signal pair to the image generator at preset time intervals; and the image generator may be configured to generate the phase image set at the preset time intervals.

In some implementations, upon receiving new phase image sets, the evaluation value calculator may be configured to discard evaluation value sets calculated based on previously received phase image sets.

In some implementations, the parallax calculator may calculate a sum of evaluation values that are respectively included in different evaluation value sets and correspond to an arbitrary candidate parallax, and may calculate a candidate parallax with the largest sum of evaluation values as the target parallax.

In some implementations, the evaluation value calculator may be configured to convert a plurality of evaluation value sets corresponding to a plurality of phase image sets into evaluation value sets corresponding to a current in-focus position of a lens included in the imaging device; and the parallax calculator may be configured to calculate the target parallax based on evaluation value sets corresponding to the current in-focus position of the lens.

In some implementations, the evaluation value calculator may be configured to calculate reliability for the evaluation value set based on noise of the phase image set; and the parallax calculator may be configured to calculate the target parallax based on the reliability.

In some implementations, the parallax calculator may be configured to calculate the target parallax based on candidate parallaxes respectively corresponding to maximum evaluation values included in different evaluation value sets.

In another aspect, an imaging device may include an imaging circuit that includes a lens and configured to collect a plurality of phase signal pairs for an object; an image generator configured to generate a plurality of phase image sets based on the plurality of phase signal pairs; an evaluation value calculator configured to calculate a plurality of evaluation value sets including evaluation values corresponding to candidate parallaxes, based on the plurality of phase image sets; and a parallax calculator configured to calculate a target parallax based on the plurality of evaluation value sets, the target parallax representing a phase shift value that allows to minimize a difference between phase images corresponding to the plurality of phase signal pairs, wherein the target parallax is a parallax that controls an in-focus position of the lens with respect to the object.

In some implementations, each of the evaluation values may indicate a degree of certainty that the candidate parallax corresponding to each evaluation value is the target parallax.

In some implementations, the plurality of phase signal pairs may be collected at different times.

In some implementations, the plurality of phase signal pairs may be collected at the same time.

It is to be understood that both the foregoing general description and the following detailed description of the present disclosure are illustrative and explanatory and are intended to provide further explanation of the disclosure as claimed.

This patent document provides implementations and examples of an imaging device for performing an autofocus function that may be used in configurations to substantially address one or more technical or engineering issues and to mitigate limitations or disadvantages encountered in some other imaging devices. Some implementations of the present disclosure relate to an imaging device for providing a phase-difference autofocus (PDAF) function that reduces the influence of noise, and a method for operating the same.

The imaging device may perform an autofocus (AF) function based on signals collected from the imaging circuit. In various implementations, the imaging device may use a phase-based autofocus function or a contrast-based autofocus function. The imaging device that performs phase-based autofocus can determine the direction and amount of positional movement of a lens based on a single frame captured through the imaging circuit. Therefore, phase-based autofocus may increase the focusing speed compared to contrast-based autofocus. However, if the captured signal includes noise, distortion of a phase image may occur, and accurate focusing may become difficult as autofocus is performed based on the distorted image.

In recognition of the issues above, the disclosed technology may provide the imaging device with an image processor that can more accurately calculate a target parallax by reducing the influence of noise. The disclosed technology may provide the image processor that can calculate an evaluation-value set including evaluation values for each of candidate parallaxes expected to be the target parallax, and may calculate the target parallax based on the calculated evaluation-value set.

Reference will now be made in detail to the embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. While the disclosure is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings. However, the disclosure should not be construed as being limited to the embodiments set forth herein.

Hereinafter, various embodiments will be described with reference to the accompanying drawings. However, it should be understood that the present disclosure is not limited to specific embodiments, but includes various modifications, equivalents and/or alternatives of the embodiments. The embodiments of the present disclosure may provide a variety of effects capable of being directly or indirectly recognized through the present disclosure.

In the following description, a detailed description of related known configurations or functions incorporated herein will be omitted to avoid obscuring the subject matter.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “includes”, “including”, and/or “comprising,” when used in this specification, specify the presence of stated constituent elements, steps, operations, and/or components, but do not preclude the presence or addition of one or more other constituent elements, steps, operations, and/or components thereof. The term “and/or” may include a combination of a plurality of items or any one of a plurality of items.

is a diagram illustrating an example structure of an imaging deviceaccording to embodiments of the present disclosure. A method of performing an autofocus (AF) function by the imaging devicewill hereinafter be described with reference to.

Referring to, the imaging devicemay include an imaging circuit, an image processor, and a motion detector.

The imaging circuitmay include an image sensorand a lens module. The image sensormay include a pixel array, a driving circuit, a timing controller, and a readout circuit.

In some implementations, the pixel arraymay include a plurality of unit pixels.

Upon receiving incident light (e.g., optical signal) that has passed through the lensincluded in the lens module, a unit pixel included in the pixel arraymay generate pixel signals corresponding to the incident light and the pixel signals may be converted into an electrical signal. Unit pixels may respectively generate electrical signals (e.g., pixel signals) corresponding to an external object(S).

Each unit pixel included in the pixel arraymay include a photoelectric conversion element that absorbs light to generate charges. The pixel signals generated by the unit pixels may correspond to charges generated by each photoelectric conversion element and the unit pixels may provide the pixel signals to the readout circuit.

In some implementations, at least some of the unit pixels included in the pixel arraymay be phase-difference pixels that generate different phase signals for the same object.

A pair of phase-difference pixels may be arranged adjacently in a vertical direction, a horizontal direction, or a diagonal direction in the pixel array to generate different phase signals for the same object. At this time, one of two phase-difference pixels corresponding to one pair of phase-difference pixels that generate different phase signals may be referred to as a first phase signal collector, and the other one of the two phase-difference pixels may be referred to as a second phase signal collector.

In addition, a signal generated by the first phase signal collector may be referred to as a first phase signal, and a signal generated by the second phase signal collector may be referred to as a second phase signal.

In some other implementations, the phase-difference pixels may include two photoelectric conversion elements that are adjacent to each other in a vertical or horizontal direction so as to generate different phase signals.

One pair of photoelectric conversion elements that generate different phase signals and are included in one phase-difference pixel may be referred to as a phase signal collector. At this time, one of two photoelectric conversion elements corresponding to one pair of photoelectric conversion elements that generate different phase signals may be referred to as a first phase signal collector, and the other one of the two photoelectric conversion elements may be referred to as a second phase signal collector. Additionally, a signal generated by the first phase signal collector may be referred to as a first phase signal, and a signal generated by the second phase signal collector may be referred to as a second phase signal.

Each of the unit pixels included in the pixel arraymay include a microlens, an optical filter, a photoelectric conversion element, and an interconnect layer (also called a wiring layer). In some implementations, one unit pixel may overlap one microlens.

The microlens may allow light incident upon the pixel arrayto converge upon the optical filter and the photoelectric conversion element. The optical filter may enable the incident light having penetrated the microlens to selectively pass therethrough based on wavelengths of the incident light.

Each unit pixel may include a photoelectric conversion element that receives incident light. The photoelectric conversion element may generate photocharges corresponding to incident light that has penetrated the microlens and the optical filter. Each of the photoelectric conversion elements may be implemented as a photodiode, a phototransistor, a photogate, a pinned photodiode (PPD), or a combination thereof. In the following descriptions, it is assumed that each photoelectric conversion element is implemented as a photodiode as an example.

If the photoelectric conversion element is a photodiode, the photoelectric conversion element may include a stacked structure in which an N-type impurity region and a P-type impurity region are vertically stacked. The photoelectric conversion element may be formed in a semiconductor substrate. For example, the semiconductor substrate may be a P-type semiconductor substrate.

The interconnect layer may be disposed below the photoelectric conversion element. Here, the interconnect layer may also be called a wiring layer as needed. The interconnect layer may include a reset transistor, a transfer transistor, a floating diffusion (FD) region, a drive transistor, a selection transistor, etc.